The present invention relates to a thermosensitive recording material in which the recording layer contains a fluorescent dye composition.
A conventional thermosensitive recording material comprises a support, for example, a sheet of ordinary paper or synthetic paper and a thermosensitive recording layer formed on the support. Colored images are formed in the recording layer by application of heat. Thermal printers provided with a thermal print head, thermal pens and infrared application devices are generally used to print on thermosensitive recording materials.
Because of their ability to form colored images by simple application of heat, such thermosensitive recording materials are widely used, not only for copying books and documents, but also for recording output information from computers, facsimile apparatus, telex and other information transmission and measuring instruments. Furthermore, such thermosensitive recording materials are employed as railway tickets and as adhesive labels for the POS (point of sales) system in supermarkets and department stores.
As a thermosensitive recording adhesive label comprising the above-mentioned thermosensitive recording material, there is known a thermosensitive recording adhesive label comprising a support, a thermosensitive recording layer formed on the front side of the support, an adhesive layer formed on the back side of the support opposite the thermosensitive recording layer, and a disposable backing sheet which is attached to the adhesive layer and which can be peeled from the adhesive layer when the thermosensitive recording adhesive label is used.
Such a thermosensitive adhesive label can be attached to a variety of commercial products. By thermally printing, for instance, a product name, price and bar code on the label, and applying the thermally printed label to products with the backing sheet removed, customers can tell from the label the name and price of the product and other information concerning the product. The thermally printed bar codes can be read by automatic reading apparatus and the information processed by computer, so that, for instance, the sale, stock and reorder of the product can be controlled. Furthermore, the label can be used for other purposes, for instance, as a merchandising marker by which customers can readily distinguish particular products from other products, for instance, for quickly identifying specially discounted products.
To improve product recognition, conventionally, a method of printing graphics, numbers, letters and bar codes with a color ink on a white thermosensitive recording label has been employed. A method of printing such figures or bar codes on a label coated with a fluorescent ink containing a fluorescent dye or pigment has also been employed. The former method, however, has the shortcomings that printing by a color ink is time-consuming and costly and the printed portions result in the formation of dust which adheres to a thermal print head in the course of thermal printing, whereafter the thermally printed portions can become smeared with such dust. When the bar code is pre-printed on the label to overcome this problem in part, there is the disadvantage that a necessary quantity of such pre-printed bar-code labels must be stocked for each product in advance.
When such thermosensitive recording adhesive labels are employed, particularly in food packaging, they may come into contact with oils (for instance, oils contained in foods) and plasticizers (for instance, plasticizers contained in plastic wrapping film). When the developed colored images come into contact with such oils and plasticizers they are frequently discolored or become blurred. Therefore, it is required that thermally printed images be prevented from being discolored or becoming blurred even if they are brought into contact with such adverse materials.